Does the new 'dynamic' C# 4.0 keyword deprecate the 'var' keyword?

Question

When C# 4.0 comes out and we have the dynamic keyword as described in this excellent presentation by Anders Hejlsberg, (C# is evolving faster than I can keep up.. I didn\'t have

Answer 1

Dynamic and var represent two completely different ideas.

var

Var essentially asks the compiler to figure out the type of the variable based on the expression on the right hand side of the assignment statement. The variable is then treated exactly as if it were explicitly declared as the type of the expression. For example the following two statements are equivalent

var a = "foo";
string a = "foo";

The key to take away here is that "var" is 100% type safe and is a compile time operation

dynamic

Dynamic is in many ways the exact opposite of var. Using dynamic is essentially eliminating all type safety for thet particular variable. It many ways it has no type. When you call a method or field on the variable, the determination on how to invoke that field occurs at runtime. For example

dynamic d = SomeOperation();
d.Foo(); // Will this fail or not?  Won't know until you run the program

The key to take away here is that "dynamic" is not type safe and is a runtime operation